/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.nulldev.util.data.CompressionAPI.thirdparty.airlift.zstd;

import static java.lang.String.format;

import java.lang.reflect.Field;
import java.nio.Buffer;
import java.nio.ByteOrder;

import com.nulldev.util.data.CompressionAPI.thirdparty.airlift.IncompatibleJvmException;

import sun.misc.Unsafe;

final class UnsafeUtil {
	public static final Unsafe UNSAFE;
	private static final long ADDRESS_OFFSET;

	private UnsafeUtil() {
	}

	static {
		ByteOrder order = ByteOrder.nativeOrder();
		if (!order.equals(ByteOrder.LITTLE_ENDIAN)) {
			throw new IncompatibleJvmException(format("Zstandard requires a little endian platform (found %s)", order));
		}

		try {
			Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
			theUnsafe.setAccessible(true);
			UNSAFE = (Unsafe) theUnsafe.get(null);
		} catch (Exception e) {
			throw new IncompatibleJvmException("Zstandard requires access to sun.misc.Unsafe");
		}

		try {
			// fetch the address field for direct buffers
			ADDRESS_OFFSET = UNSAFE.objectFieldOffset(Buffer.class.getDeclaredField("address"));
		} catch (NoSuchFieldException e) {
			throw new IncompatibleJvmException("Zstandard requires access to java.nio.Buffer raw address field");
		}
	}

	public static long getAddress(Buffer buffer) {
		if (!buffer.isDirect()) {
			throw new IllegalArgumentException("buffer is not direct");
		}

		return UNSAFE.getLong(buffer, ADDRESS_OFFSET);
	}
}
